Method of treating metals



Patented Mar. 23, 1937 UNITED STATES METHOD OF TREATING METALS Harvey Ross Balding, Vandergrift, Pa., assignor to American Sheet and Tin Plate Company, a corporation of New Jersey No Drawing.

Application June 17, 1935, Serial 2 Claims.

This invention relates to a method of treating metals, and more particularly those which serve as a base for the application of vitreous enamel coatings.

5 In the manufacture of enamel ware, it has for some time been the practice to form, or draw, sheet steel and thereafter apply a vitreous enamel coating thereto. The coating is fused, or sintered, onto the base metal by the application of heat in any suitable manner, but numerous difliculties frequently arise at this stage of the process. One of these diiiiculties is the formation during the fusing operation of objectionable defects in the surface of the enamel which is known as reboilmg" and is brought about by the condition of the base metal. These reboiling difliculties are due to bubbles of gas which are released from the base metal by the heating operation, and obviously mar the desired surface condition of the finished enamel article.

It also very frequently happens that this gas released from the surface of the base metal by the heating operation causes an opening in the surface of the enamel to form other defects 5 which are known in the art as copper heads or fish scaling". These defects in the art of applying vitreous enamel coatings are not consistent, as they vary with the condition of the coating material and its time and temperature for fusing,

which, of course, change throughout the various fabricating plants.

It is among the objects of the present invention to provide a novel method of treating metals which are intended for the subsequent application of vitreous enamel coatings in which there is a complete absence of reboiling" or any tendency toward it.

Another object is the provision of a method of the class described which will eliminate the "sensi- 40 tivity of practice in various fabricating plants notwithstanding minor variations in the condition of the coating material, firing time, and temperatures, which frequently give rise to the appearance of the defects previously discussed.

Another object is the provision of a novel method of the class described which may be easily and cheaply practiced withexisting types of equipment to obtain very good results.

In its broadest sense the method provides for 5 the complete deoxidation or killing of the metal while in a molten state and within a time interval which minimizes the inclusion therein of gases.

The proposition of killing the molten metal is, of course, very old in the art and generally carried out by the addition to the ladle of aluminum, ferro-silicon or other deoxidizers, as the molten metal is being tapped from the melting furnace thereinto.

I have found that the addition of aluminum to the mold, or even the ladle, will not prevent reboiling when the metal is provided with vitreous enamel coatings, contrary to expectation.

The method of the invention distinguishes over the prior art in that the molten metal is killed by the sole addition to the mold, and during the teeming" of the molten metal thereinto from the ladle, of silicon only, in the form of ferro-silicon or refined silicon.

It is well known in the art that aluminum is a more powerful and complete killing agent than silicon, but I have found that the addition of silicon-and-aluminum either to the ladle or mold will not produce a metal having non-reboiling characteristics. This is true regardless of the sequence of adding silicon-and-aluminum, whether mixed or otherwise.

Metals of the type described (intended for the subsequent application of vitreous enamel coatings) are usually of the low metalloid variety and contain less than 0.10 per cent carbon and 0.50 per cent manganese. In practicing my invention I may produce steel for subsequent enameling which has a carbon content of approximately 9.025 per cent and a manganese content of approximately 0.08 per cent. This steel is then poured in its molten condition from a refining furnace into a ladle, which is identified in the art as the tapping" operation. As the molten steel is being teemed from the ladle into the mold, silicon (in the form of ferro-silicon or refined silicon) is added to the mold, resulting in the rapid and effective killing of the steel at this point of its manufacture.

As a specific instance, a very satisfactory result has been obtained by adding approximately two pounds of per cent ferro-silicon to the mold for each net ton of steel being treated, and while the latter is being teemed. The addition of the ferro-silicon to the mold may be gradual (whether intermittent or otherwise), if desired. It is to be understood that the amount of silicon added in the manner previously described may be reduced somewhat if the steel is higher in carbon or manganese. silicon contains less than 90 per cent available silicon its ratio must be increased. I have found that the more expensive alloy of higher silicon Also, for instance, if the ferroi content is much to be preferred, as the "killing" action is more rapid and pronounced;

After the steel has been completely "killed" it. is subsequently processed to desired form or shape according to any oi the well known practices.

If, by way of example, enameled sheets are intended as the final article, the uncoated sheets are subjected to the usual coating of vitreous enamel which is fused thereon by firing or heating in a suitable furnace to a temperature of from 1550 degrees Fahrenheitto 1625 degrees Fahrenheit, and then permitted to cool to room temperature. After the coating of vitreous enamel has cooled, at least one final covering coatof vitreous enamel is usually applied thereto. If this covering coat is applied, the sheet is again fired or heated to burn it on the metal. It is during this firing or heating that the metal reboils" and develops gas "bubbles" or the "copper-heads" or fish scales"- previously mentioned. Due to the treatment of the molten metal in accordance with the teaching of the present invention, a vitreous enameled article is obtained having a perfectly smooth and 26 uninterrupted surface condition. The preferred method of rolling strip metal is usually in the direction of the axis of the original ingot, and if this is followed, the metal resulting from the foregoing treatment will consistently so produce excellent results. If, on the other hand,

the equipment of the mill is such as to necessitate the rolling ofthe strip in a direction which is transverse to the axis of the original ingot, the metal produced by the method of the invention 35 has a somewhat increased tendency toward a seamy surface.

While these resultant seams are in no way connected with reboiling characteristics, they nevertheless are sometimes objectionable from the 40 standpoint of appearance after enameling. If it isnecessarytoprocessthemetalinthismanner, and seams result, I have found that they may be expeditiously removed by bombarding an abrasive upon them. This abrasive (as. for example, grit) removes'the seamstosuchanextentthat theyare no longer objectionable. This bombardment with an abrasive is an inexpensive operation (as it, of course, obviates the necessity of the usual pickling operation) and may be of short duration, as ,the seams,ifany, will bevery shallow.

Iron or steel made after the manner of my invention will usually contain from 0.015 to 0.10 per cent silicon, but it is the presence in the iron or steel of silicon in approximately such amounts, which silicon has been added to the steel in the particular manner! have described. that produces the improvement which I claim for my process.

rather than the mere presence of silicon as such killed steel into articles, and coating the articles with vitreous enamel.

2. The method which comprises teeming molten steel into a mold, killing the molten steel during the teeming step solely by the use of silicon. forming the killed steel into articles, and coating the articles with vitreous enamel,

- HARVEY ROSBBELDING. 

